MECHANISM FOR POSITIONING TRACTORS

Apparatus for use with a printer which has a pair of tractors that engage sprocket holes in the paper to adjust for different paper widths or to adjust the lateral position of the paper. The apparatus comprises a pair of coaxial lead screws (25, 26) one (25) attached to a rotatable shaft (29) and the second (26) rotatable on the shaft (29) adjacent to and relative to the one lead screw (25). One tractor is coupled to each lead screw (25, 26). Rotation of the one lead screw (26) is obtained by a knob (30) keyed to an end of the rotatable shaft (29). Rotation of the second lead screw (26) is prevented during rotation of the knob (30) by spring loaded fingers (31a) with detent elements engageable with detention gearing (26c) on the end of the second lead screw (26). Rotation of both screws (25, 26) is obtained by rotation and axial movement of the knob (30) on the shaft so that a cam surface on the knob engages cam means of the spring fingers (31a) to disengage detent elements from the detention gearing and drive gearing on the knob (30) engages drive gearing on the second lead screw (26).